Optical assemblies

ABSTRACT

Provided are optical assemblies which allow for optical and mechanical connection between an optical bench and an optical fiber connector. The invention finds particular applicability in the optoelectronics industry in forming micro-optical components.

This application claims the benefit of priority under 35 U.S.C. § 119(e)to U.S. Provisional Application No. 60/686,543, filed Jun. 1, 2005, theentire contents of which are incorporated herein by reference.

The present invention relates generally to the field of optoelectronics.In particular, the present invention relates to optical assemblies whichallow for optical and mechanical connection between an optical bench andoptical fiber connector. The invention finds particular applicability tothe manufacture of a micro-optical component assembly which includes ahousing for an optoelctronic subassembly such as a transmitter, receiveror transceiver optical subassembly, and which can be connected with anoptical fiber connector.

Optoelectronic devices such as lasers and photodetectors are used for avariety of applications, for example, in the telecommunicationsindustry. Existing commercial transmitter optical subassemblies (TOSAs)are manufactured using a process based on a TO-can header assemblycontaining a laser diode and monitor diode. A typical TO-can typepackage is described, for example, in U.S. Patent ApplicationPublication No. US 2004/0240497 A1. The header assembly also has anoptically transparent window or lens, allowing an optical signal to passto or from the optoelectronic device. In order to focus the laser lightinto an optical fiber ferrule, conventional TO-can TOSA packagesincorporate a variety of cylindrical machined subcomponents which mustbe aligned with each other, and welded or bonded in place. At least twoseparate alignment and welding or bonding steps are required for such apackage. In devices requiring an optical isolator, further alignment andwelding or bonding is required. In fabricating a conventional TO-canTOSA package, costly tooling in the form of laser welding or bondingsystems is required. In addition, TO-can packages are generally not wellsuited for packaging of planar-type device structures such as siliconoptical bench.

It would therefore be beneficial to provide an optical assembly in whichthe number of components, alignment steps and welding or bonding stepsis reduced. For example, it would be desirable to reduce the number ofalignment and welding or bonding steps to a single alignment and weldingor bonding step. As a result, significant cost savings in materials,labor and tooling over conventional optical assemblies could beattained. It would also be desirable to provide an optical assemblywhich would be suitable for use with silicon optical bench structures.

In accordance with a first aspect of the invention, an optical assemblyis provided. The optical assembly includes: an optical bench comprisingan optoelectronic component affixed to a substrate; a housing in whichthe optical bench is disposed, the housing comprising a first matingregion; an optical ferrule receptacle for optically coupling the opticalbench with an optical fiber, the optical ferrule receptacle comprising asecond mating region, wherein the housing and the optical ferrulereceptacle are mated with each other at the first and second matingregions; and a flex circuit attached to the optical bench wherein theflex circuit is disposed in contact with an interior surface of thehousing for relieving strain in the flex circuit.

As used herein, the terms “a” and “an” are inclusive of “one or more”.The term “on” and “over” are used interchangeably in defining spatialrelationships, and encompass the presence or absence of interveninglayers or structures. Also as used herein, the term “optical assembly”encompasses structures having optical and/or optoelectronicfunctionality.

The present invention will be discussed with reference to the followingdrawings, in which like reference numerals denote like features, and inwhich:

FIG. 1 illustrates an exemplary optical assembly in accordance with theinvention;

FIG. 2 illustrates a first exploded view of the optical assembly shownin FIG. 1;

FIG. 3 illustrates a second exploded view of the optical assembly shownin FIG. 1 from a direction opposite that shown in FIG. 2; and

FIG. 4 illustrates an upper housing portion of an optical assembly inaccordance with a further aspect of the invention.

The present invention will now be described with reference to FIGS. 1-3,depicting an exemplary optical assembly 1 in accordance with the presentinvention. The optical assembly includes an optical bench 3. The opticalbench includes a substrate 5 having an upper surface 7 in/on whichvarious surface features are formed. The substrate 5 is typically formedfrom a semiconductor material which may be in wafer or chip form, suchas silicon, for example, <100> single-crystal-silicon, gallium arsenide,indium phosphide, or lithium niobate, or from a ceramic, polymer, ormetal. One or more optical and/or optoelectronic components are bondedto the substrate upper surface 7. Typical optical components include,for example, optical fibers, lenses such as ball lenses, filters, andoptical isolators. The exemplified optical isolator includes permanentmagnets 8 a and garnet crystal 8 b. Typical optoelectronic devicesinclude, for example, laser die and photodetectors. The optical andoptoelectronic components of the optical bench are shown generally as adashed line in the illustrations.

The substrate upper surface 7 includes one or more surface featuresformed therein or on for holding the various components. The surfacefeatures may include, for example, grooves such as V- or U-groove forholding an optical fiber, pits for holding lenses such as a ball lens,and metal features for electrical connection of the optoelectronicdevice. Typical metal features include, for example, contact pads towhich the optoelectronic device is soldered, metal lines and bondingpads for connection to a power supply. Techniques for forming surfacefeatures are known to those skilled in the art. For example, grooves andpits may be formed using masking and wet and/or dry etching techniques,while metallization structures may be formed by sputtering, evaporationor plating techniques. These techniques may optionally be used to form asubstrate master from which substrates may be formed in a moldingprocess. A lid 9 may further be provided for the optical bench forforming a hermetically enclosed volume for the components.

Electrical connection to the optical bench 3 may be accomplished by anyknown means. In the exemplified embodiment, a flex circuit 11 isprovided for this purpose. Bonding pads (not shown) of the flex circuit11 are soldered to corresponding bonding pads on the underside of theoptical bench 3, which in turn are electrically connected to theoptoelectronic device of the optical bench.

A housing 13 for the optical bench provides one or more functionsincluding, for example, alignment when assembling the optical assembly,heat sinking to remove unwanted heat generated by the optoelectronicdevice, strain relief to relieve stress from the flex circuit,mechanical protection for the optical bench, mounting capability to aprinted circuit board or other electronic substrate, and thermalisolation to prevent solder reflow in earlier-formed solder jointsduring later soldering processes. The optical bench housing 13 may beconstructed, for example, of machined, molded or stamped metal orplastic, including thermally conductive plastic. The optical benchhousing may be formed of a plurality of pieces as in the embodimentshown in FIGS. 1-3. In the exemplified embodiment, the housing includesan upper portion 15 and lower portion 17. The housing includes analignment hole 19 for receiving an optical ferrule receptacle 21. Inaccordance with one embodiment of the invention, when connectedtogether, a symmetrical relationship between the housing and opticalferrule receptacle mating portions is created. The housing parts mayinclude surface features which allow for passive alignment between thehousing parts and between the housing parts and other components. Forexample, alignment pins 23 may be provided for passively locating flexcircuit 11. A trench 25 and elevated regions 26 in the lower housingportion 13 for passively locating the optical bench 3 may be provided.

The flex circuit 11 is in contact with the lower housing portion 17. Arelief trench 28 may be provided in this section for providing an airgap between the flex circuit and lower housing portion. This air gapacts as a thermal stop to protect solder joints formed between the flexcircuit and optical bench 3 from reflowing when subsequently solderingthe optical bench to the housing. The lower and/or upper housingportions 17, 15 may further include a strain relief land surface 29 forrelieving strain in the flex circuit 11. As the housing upper and lowerportions 15, 17 are assembled, surfaces 29 contact the flex circuit,providing strain relief for the flex circuit. Pins 31 shown protrudingfrom the land surface 29 may be provided for mating with holes 32 in theflex circuit to provide an optional additional registration. Compliantmaterials such as foams or adhesives may also be added on relief landsurface 29 and/or on the flex circuit 11 to sandwich and support theflex circuit as it exits the housing 13.

The housing 13 may optionally include provision for holding one or morecomponents, such as one or more of the above-described opticalcomponents (e.g., optical fibers, lenses such as ball lenses, filters,and optical isolators). Such a structure may allow for a package havinga smaller footprint and/or provide improved manufacturability. FIG. 4,for example, illustrates an upper housing portion 15 in which apermanent magnet 8 a, which forms a portion of an optical isolator, hasbeen incorporated. One may additionally or optionally include the garnetcrystal 8 b (see FIGS. 2 and 3) of the optical isolator and/or multipleisolator magnets in the housing.

The optical ferrule receptacle 21 is provided for optically andmechanically mating to an optical fiber connector (not shown) containingan optical fiber or fiber stub. The optical fiber connector is attachedto an optical fiber pigtail. Optical ferrule receptacle 21 is typicallymade of a metal or plastic on the outside, and typically contains asplit ceramic sleeve to align with the connector. The optical receptaclemay contain a double sided polished ferrule stub with a length ofoptical fiber in it, such as is commercially available, for example,from Kyocera Corporation. The optical receptacle may include a wick stop27 for preventing excess bonding agent from entering the optical path.As illustrated, the wick stop may take the form of a closed groove inthe face of the optical receptacle between the mating region and theoptical path. While the illustrated wick stop 27 is circular, othergeometries may be employed.

Connection of the housing 15 to the optical ferrule receptacle 21 isfacilitated with a bonding agent. Suitable bonding agents include, forexample, epoxies such as UV curing, thermal curing, and dual cureepoxies, and solders. Beneficially, the bonding agent may be kept out ofthe optical path of the assembly. In this way, bonding agents that wouldotherwise be unusable due, for example, to optical loss issues, may beemployed. Application of the bonding agent may be controlled such thatit may be symmetrically dispensed between the mating region 19 of thehousing 15 and the mating region 30 of the optical receptacle assembly21. The symmetrical relationship between the housing and opticalreceptacle mating regions minimizes variations in shrink and swelling ofthe bonding agent during cure and due to environmental exposure,resulting in minimal impact on the alignment to the optical bench 3.

1. An optical assembly, comprising: an optical bench comprising anoptoelectronic component affixed to a substrate; a housing in which theoptical bench is disposed, the housing comprising a first mating region;an optical ferrule receptacle for optically coupling the optical benchwith an optical fiber, the optical ferrule receptacle comprising asecond mating region, wherein the housing and the optical ferrulereceptacle are mated with each other at the first and second matingregions; and a flex circuit attached to the optical bench wherein theflex circuit is disposed in contact with an interior surface of thehousing for relieving strain in the flex circuit.
 2. The opticalassembly of claim 1, wherein the optical bench is a silicon opticalbench comprising a silicon substrate.
 3. The optical assembly of claim1, wherein the optical bench is itself hermetically sealed.
 4. Theoptical assembly of claim 1, wherein the interior surface of the housingincludes a trench providing an air gap between the housing and a portionof the flex circuit.
 5. The optical assembly of claim 1, wherein theinterior surface of the housing includes alignment pins for passivelylocating the flex circuit.
 6. The optical assembly of claim 1, furthercomprising a bonding agent for bonding the optical ferrule assembly tothe housing, wherein the optical ferrule assembly and/or the housingcomprises a wick stop for preventing the bonding agent from entering theoptical path during the bonding of the optical ferrule assembly to thehousing.
 7. The optical assembly of claim 1, wherein the housingcomprises an upper housing portion connected to a lower housing portion,the upper and lower portions each comprising a portion of the firstmating region.
 8. The optical assembly of any of claim 1, wherein thefirst mating region is radially symmetrical to the second mating region.9. The optical assembly of any of claim 1, further comprising an opticalcomponent or a portion thereof mounted to the housing.
 10. The opticalassembly of claim 9, wherein a magnet forming a portion of an opticalisolator is mounted to the housing.